1. Field of the Invention
The present invention relates to satellites. More specifically, the present invention relates to systems and methods for observing and inspecting satellites.
2. Description of the Related Art
A considerable investment has been made to place satellites in geosynchronous orbit (GEO) to perform a variety of functions. Geosynchronous satellites are satellites with an orbital track on the Earth that repeats regularly over points on the Earth over time. Geosynchronous satellites located at the equator appear stationary over the Earth and hence are referred to as ‘Geostationary’.
Geosynchronous satellites periodically encounter problems and anomalies and are also subject to attack. Hence, there is a need to inspect geosynchronous satellites and other objects in space to determine the status thereof. This may include detection and resolution of anomalies on spacecraft. Detecting new objects, verifying the position and velocity of existing objects, and collecting imagery of objects serve a number of military, civil, and commercial needs. For example, this information could be useful to avoid collisions in space and understand the operating status of satellites.
Currently, this information is collected from the ground and from space based platforms in low earth orbit (LEO). Unfortunately, collection of information from ground-based assets and LEO is difficult for satellites at long range. The vast majority of satellites in geosynchronous (24-hour) orbits are at approximately 35,800 km altitude. Ground-based electro-optic assets can detect some objects at this altitude, but telescope sizes limit the ability to collect high-resolution imagery. In principle, ground-based radar systems can collect high-resolution imagery independent of the range to the target using inverse synthetic aperture techniques. However, the extremely small ground velocity of most satellites at GEO makes this difficult or impossible in practice.
Some have considered placing satellites in GEO-like orbits with a number of sensor types to collect data and image satellites. See, for example, U.S. Pat. No. 4,387,391 entitled SATELLITE INSPECTION SYSTEM USING HOVERING-TYPE INTERCEPTORS, issued Jun. 7, 1983 to K. J. Hecker, the teachings of which are hereby incorporated herein by reference. These approaches typically allow detailed monitoring of only one satellite over a long time period. That is, the nearly coincident orbits of the observer and target satellites result in time periods on the order of hours to collect synthetic aperture imagery and do not enable collection of information large numbers of satellites.
It is also difficult to maintain optimal range separation for imaging while controlling relative velocity due to orbital dynamics. For example, an observer that wishes to stay within ˜100 km of a target satellite will have a relative velocity of less than 10 meters/second and will drift through the entire GEO belt in approximately nine (9) months. Hence, it would take a long time to observe a large number of satellites.
There is an unfilled need to be able to monitor and image these satellites on a regular basis. That is, there is a need in the art for an improved system or method for frequently revisiting orbital assets to detect and characterize the status thereof.